[CH3:1][C:2]([NH:4][CH2:5][CH2:6][C:7]1[C:11]2[CH:12]=[C:13]([O:16][CH3:17])[CH:14]=[CH:15][C:10]=2[NH:9][CH:8]=1)=[O:3].B.[OH-].[K+].[C:21](OC(=O)C)(=[O:23])[CH3:22]>FC(F)(F)C(O)=O.N1C=CC=CC=1.O>[C:21]([N:9]1[C:10]2[C:11](=[CH:12][C:13]([O:16][CH3:17])=[CH:14][CH:15]=2)[CH:7]([CH2:6][CH2:5][NH:4][C:2](=[O:3])[CH3:1])[CH2:8]1)(=[O:23])[CH3:22]
To a solution, cooled to 0° C., of melatonin (1 mmol) in trifluoroacetic acid (2 ml) is added dropwise borane (2 eq, 1M solution in THF). The mixture is stirred for 30 min at 0° C. followed by dropwise addition of water (1.5 ml), and the medium is left stirring for 1 h at room temperature. The mixture is then brought to pH=10 using 2N potassium hydroxide solution and is then extracted with dichloromethane. The crude product is separated on a column of flash silica (25/75/5 acetone/dichloromethane/methanol) and 110 mg of N-[2-(5-methoxyindolin-3-yl)ethyl]acetamide are obtained, which product is then acetylated with acetic anhydride in pyridine to give N-[2-(1-acetyl-5-methoxyindolin-3-yl)ethyl]acetamide.
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